Derivatives of 4-aminoantipyrine as anti-Alzheimers butyrylcholinesterase inhibitors

ABSTRACT

One embodiment of the invention relates to the treatment of diseases associated with increased butyrylcholinesterase (BuChE) enzyme activity such Alzheimer&#39;s Disease (AD), involving administering an effective amount of a compound selected from a group of new N, N′-disubstituted benzylamine derivatives (1-8) of 4-aminoantipyrine (ampyrone). The kinetic studies of two potent compounds 4-(Bis(4-iodobenzyl) amino)-1,5-dimethyl-2-phenyl-1,2-dihydro-3H-pyrazol-3-one (5) (IC 50 =2.43±0.4 and Ki=5.67±0.5 μM) and 4-(Bis(2-bromobenzyl) amino)-1,5-dimethyl-2-phenyl-1,2-dihydro-3H-pyrazol-3-one (6) (IC 50 =0.7±0.2 and Ki=2.4±0.4 μM), revealed them as a competitive and a non-competitive inhibitor of BuChE, respectively. Galantamine Hydrobromide was used as standard inhibitor with IC 50 =40.83±0.4 and Ki=21.5±0.7 μM (Mixed type Inhibitor). The metabolite of aminophenazone, 4-aminoantipyrine (A) is also being reported here as an inhibitor of BuChE for the first time.

BACKGROUND OF THE INVENTION

4-Aminoantipyrine (A) is a metabolite of aminophenazone (drug being used as anti-inflammatory in the past. Which was withdrawn due to its adverse effects of agranulocytosis), is an aromatic compound with analgesic, antipyretic, and anti-inflammatory properties. The pharmacological activities of 4-Aminoantipyrine (A) derivatives includes analgesic, antimicrobial, and antiviral properties.

The current study relates to the synthesis of eight new N, N′-disubstituted benzylamine derivatives of 4-aminoantipyrine (A), and evaluation of their in vitro BuChE inhibition activity.

Alzheimer's disease (AD) is an acute neurological disorder, which causes behavioral and cognitive dysfunctions. The disease is managed by the inhibition of cholinesterase (ChE) enzymes, acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE). In a healthy brain acetylcholinesterase (AChE) plays a major role while butyrylcholinesterase (BuChE) is known for the minor role. However, in Alzheimer's Disease (AD) the increased level of (BuChE) found with the decline or unchanged level of AChE activity. Therefore, butyrylcholinesterase (BuChE) inhibitors are used as possible treatment of AD.

Donepezil, galanthamine, and rivastigmine are frequently used inhibitors of cholinesterase (ChE) enzymes. These inhibitors are associated with several side effects such as, diarrhea, insomnia, anorexia, weight loss, and esophageal rupture.

BRIEF SUMMARY OF THE INVENTION

The present invention relates to the synthesis of eight new derivatives of 4-aminoanitpyrine (A) and evaluation of their BuChE inhibition activity. The newly synthesized compounds were found to be the potent in vitro inhibitors of (BuChE) enzyme, in comparison with the standard drug galantamine hydrobromide (IC₅₀=40.83±0.4 which can be further studied for the management and treatment of AD.

DETAILED DESCRIPTION OF THE INVENTION

Synthesis: N, N′-Disubstituted benzylamine derivatives of 4-aminoantipyrine (A) 1-8 were synthesized through microwave reactor in 1-3 min at 220° C., and power 900 W, in the presence of base K₂CO₃ and substituted benzyl bromide in 2 mL DMF as describe in following reaction scheme.

Reaction Scheme:

4-(Bis(3-chlorobenzyl) amino)-1,5-dimethyl-2-phenyl-1,2-dihydro-3H-pyrazol-3-one (1): Mp: 200-201° C.; IR (KBr, cm⁻¹): 1654 (C═O), 1592, 1488 (C═C), 1083.1 (C—Cl); EI-MS (direct probe, positive EI) m/z: 453.2 [M+2]⁺, 451.2 [M⁺], 326.1; HREI-MS m/z: Calculated for C₂₅H₂₃Cl₂N₃O: 451.1218, Observed: 451.1224; ¹H-NMR (400 MHz, DMSO-d₆) δ: 7.45 (t, J_(5″,4″/5″,6″)=J_(5′″,4′″/5′″,6′″)=8 Hz, 2H, H-5″, H-5′″), 7.29 (ovp, 11H, H-2′, H-3′, H-4′, H-5′, H-6′, H-2″, H-4″, H-6″, H-2′″, H-4′″, H-6′″), 4.13 (s, 4H, 2CH₂), 2.74 (s, 3H, N—CH₃), 1.71 (s, 3H, CH₃).

4-(Bis(2-chlorobenzyl) amino)-1,5-dimethyl-2-phenyl-1,2-dihydro-3H-pyrazol-3-one (2): Mp: 211-212° C.; IR (KBr, cm⁻¹): 1653 (C═O), 1590, 1529 (C═C), 1046 (C—Cl); EI-MS (direct probe, positive EI) m/z: 453.2 [M+2]⁺, 451.2 [M⁺], 326.1; HREI-MS m/z: Calculated for C₂₅H₂₃Cl₂N₃O: 451.1218, Observed: 451.1204; ¹H-NMR (400 MHz, DMSO-d₆) δ: 7.47 (t, J_(3′,2′/3′,4′)=J_(5′,4′/5′,6′) 8 Hz, 2H, H-3′, H-5′), 7.37 (m, 4H, H-2′, H-6′, H-3″, H-3′″), 7.28 (m, 7H, H-4′, H-4″-H-6″, H-4′″-H-6′″), 4.27 (s, 4H, 2CH₂), 2.71 (s, 3H, N—CH₃), 1.50 (s, 3H, CH₃).

4-(Bis(3-iodobenzyl) amino)-1,5-dimethyl-2-phenyl-1,2-dihydro-3H-pyrazol-3-one (3): Mp: 203-204° C.; IR (KBr, cm⁻¹): 1648 (C═O), 1619, 1590 (C═C), 849.8 (C═I); EI-MS (direct probe, positive EI) m/z: 635.3 [M⁺], 508.3, 417.9; HREI-MS m/z: Calculated for C₂₅H₂₃I₂N₃O: 634.9930, Observed: 634.9943; ¹H-NMR (400 MHz, DMSO-d₆) δ: 7.61 (s, 2H, H-2″, H-2′″), 7.57 (d, J_(4″,5″)=J_(4′″,5′″)=5.4 Hz, 2H, H-4″, H-4″), 7.46 (t, J_(3′,2′/3′,4′)=J_(5′,4′/5′,6′)=8 Hz, 2H, H-3′, H-5′), 7.27 (m, 5H, H-2′, H-4′, H-6′, H-6″, H-6′″), 7.10 (t, J_(5″,4″/5″,6″)=J₅′″,4′″/5′″,6′″=7.8 Hz, 2H, H-5″, H-5′″), 4.08 (s, 4H, 2CH₂), 2.74 (s, 3H, N—CH₃), 1.66 (s, 3H, CH₃).

4-(Bis(2-iodobenzyl) amino)-1,5-dimethyl-2-phenyl-1,2-dihydro-3H-pyrazol-3-one (4): Mp: 221-222° C.; IR (KBr, cm⁻¹): 1653 (C═O), 1615, 1589, (C═C), 838A (C—I); EI-MS (direct probe, positive EI) m/z: 635.3 [M⁺], 508.3, 417.9; HREI-MS m/z: Calculated for C₂₅H₂₃I₂N₃O: 634.9930, Observed: 634.9959 ; ¹H-NMR (400 MHz, DMSO-d₆) δ: 7.81 (d, J_(3″,4″)=J_(3′″,4′″)=8 Hz, 2H, H-3″, H-3′″), 7.46 (t, J_(3′,2′/3′,4′)=J_(5′,4′/5′,6′)=8 Hz, 2H, H-3′, H-5′), 7.37 (d, J_(2′,3′)=J_(6′,5′)=8 Hz, 2H, H-2′, H-6′), 7.30 (m, 5H, H-2′, H-4′, H-5″, H-6″, H-5′″, H-6′″), 6.99 (t, J_(4″,3″/4″,5″)=J_(4′″,3′″/4′″,5′″)=8 Hz, 2H, H-4″, H-4′″), 4.25 (s, 4H, 2CH₂), 2.71 (s, 3H, N—CH₃), 1.50 (s, 3H, CH₃).

4-(Bis(4-iodobenzyl) amino)-1,5-dimethyl-2-phenyl-1,2-dihydro-3H-pyrazol-3-one (5): Mp: 220-221° C.; IR (KBr, cm⁻¹): 1660 (C═O), 1590, 1484 (C═C), 880.1 (C—I); EI-MS (direct probe, positive EI) m/z: 635.3 [M⁺], 508.3, 417.9; HREI-MS m/z: Calculated for C₂₅H₂₃I₂N₃O: 634.9930, Observed: 634.9939 ; ¹H-NMR (400 MHz, DMSO-d₆) δ: 7.64 (d, J_(3″,2″)=J_(5″,6″)=J_(3′″,2′″)=J₅′″,6′″ 8 Hz, 4H, H-3″, H-5″, H-3′″, H-5′″), 7.45 (t, J_(3′,2′/3′,4′)=J_(5′,6′/5′,4′)=8 Hz, 2H, H-3′, H-5′), 7.27 (m, 3H, H-2′, H-4′, H-6′), 7.09 (d, J_(2″,3″)=J_(6″,5″)=J_(2′″,3′″)=J_(6′″,5′″)=8 Hz, 4H, H-2″, H-6″, H-2′″, H-6′″), 4.06 (s, 4H, 2CH₂), 2.76 (s, 3H, N—CH₃), 1.72 (s, 3H, CH₃). ¹³C-NMR (100 MHz, DMSO-d₆) δ 164.0 (C═O), 154.0 (C-5), 138.6 (C-1″, C-1′″), 135.2 (C-1′), 120.0 (C-4″, C-4′″), 117.5 (C-4), 131.0 (C-2″, C-6″, C-2′″, C-6′″) 131.0 (C-3″, C-5″, C-3′″, C-5′″) 129.0 (C-3′, C-5′), 125.8 (C-4′), 123.0 (C-2′, C-6′) 56.5 (2CH₂), 36.0 (N—CH₃), 9.7 (CH₃).

4-(Bis(2-bromobenzyl) amino)-1,5-dimethyl-2-phenyl-1,2-dihydro-3H-pyrazol-3-one (6): p: 201-202° C.; IR (KBr, cm⁻¹): 1651 (C═O), 1590, 1492 (C═C), 1025.4 (C—Br); EI-MS (direct probe, positive EI) m/z: 543.1 [M+4]⁺, 541.1 [M+2]⁺, 539.02 [M⁺], 460.1, 371.9; HREI-MS m/z: Calculated for C₂₅H₂₃Br₂N₃O: 539.0208, Observed: 539.0180; ¹H-NMR (400 MHz, DMSO-d₆) δ: 7.55 (d, J_(3″,4″)=J_(3′″,4′″)=7.6 Hz, 2H, H-3″, H-3′″), 7.45 (t, J_(3′,2′/3′,4′)=J_(5′,4′/5′,6′)=7.6 Hz, 2H, H-3′, H-5′), 7.38 (d, J_(3″,4″)=J_(3′″,4′″)=7.6 Hz, 2H, H-2′, H-6′), 7.27 (m, 5H, H-4′, H-5″, H-6″, H-5′″, H-6″), 7.15 (t, J_(4″,3″/4″,5″)=J₄′″,3′″/4′″,5′″=7.6 Hz, 2H, H-4″, H-4′″) 4.25 (s, 4H, 2CH₂), 2.70 (s, 3H, N—CH₃), 1.49 (s, 3H, CH₃).

4-(Bis(4-bromobenzyl) amino)-1,5-dimethyl-2-phenyl-1,2-dihydro-3H-pyrazol-3-one (7): Mp: 231-232° C.; IR (KBr, cm⁻¹): 1666.9 (C═O), 1596, 1545, 1509 (C═C), 1007 (C—Br); EI-MS (direct probe, positive EI) m/z: 543.1 [M+4]⁺, 541.1 [M+2]⁺, 539.02 [M⁻], 460.1, 371.9; HREI-MS m/z: Calculated for C₂₅H₂₃Br₂N₃O: 539.0208, Observed: 539.0176; ¹H-NMR (400 MHz, DMSO-d₆) δ: 7.48 (m, 6H, H-3′, H-5′, H-3″, H-5″, H-3′″, H-5′″), 7.24 (m, 7H, H-2′, H-4′, H-6′, H-2″, H-6″, H-2′″, H-6′″), 4.08 (s, 4H, 2CH₂), 2.76 (s, 3H, N—CH₃), 1.72 (s, 3H, CH₃). ¹³C-NMR (100 MHz, DMSO-d₆) 67 163.0 (C═O), 154.1 (C-5), 138.6 (C-1″, C-1′″), 135.2 (C-1), 119.9 (C-4″, C-4″), 117.5 (C-4), 131.1 (C-2″, C-6″, C-2′″, C-6′″) 130.9 (C-3″, C-5″, C-3′″, C-5″') 128.9 (C-3′, C-5′), 125.8 (C-4′), 123.0 (C-2′, C-6′) 56.5 (2CH₂), 36.0 (N—CH₃), 9.7 (CH₃).

4-(Bis(3-bromobenzyl) amino)-1,5-dimethyl-2-phenyl-1,2-dihydro-3H-pyrazol-3-one (8): Mp: 241-242° C.; IR (KBr, cm⁻¹): 1679 (C═O), 1596, 1545, 1509 (C═C), 1059 (C—Br): EI-MS (direct probe, positive EI) m/z: 543.1 [M+4]⁺, 541.1 [M+2]⁺, 539.02 [M⁺], 460.1, 371.9; HREI-MS m/z: Calculated for C₂₅H₂₃Br₂N₃O: 539.0208, Observed: 539.0205; ¹H-NMR (400 MHz, DMSO-d₆) δ: 7.46 (m, 6H, H-3′, H-5′, H-2″, H-4″, H-2′″, H-4′″), 7.28 (m, 7H, H-2′, H-4′, H-6′, H-5″, H-6″, H-5′″, H-6′″), 4.29 (s, 4H, 2CH₂), 2.75 (s, 3H, N—CH₃), 1.70 (s, 3H, CH₃).

Material

4-Aminoantiyprine (A) was purchased from Alfa Aesar (Heysham, UK), 3-chloro, 3-iodo, 2-iodo, and 4-iodo benzyl bromide was purchased from Mreda Technology Inc (USA) and Innochem (UAE). 2-Bromo, 4-bromo, 2-chloro and 3-bromo benzyl bromide were purchased from Innochem (UAE).

Electron impact mass spectroscopy (EI-MS), was done by JEOLJMS-600H mass spectrometer (Japan). 300 and 400 MHz Bruker Avance NMR spectrometers (Switzerland) were used to record the NMR spectra. Melting point of the synthesized analogues were recorded by using Buchi M-560 (Japan). FTIR-8900 (Shimadzu, Japan) was used to analyze the IR spectra of the synthesized compounds through KBr disc.

Methods Protocol for In-vitro Butyryl Cholinesterase Activity

In-vitro butyryl cholinesterase inhibitory activity was performed in 96-well microplates, 0.5 mM test compound in methanol, was incubated with 20 μL butyrylcholinesterase, and 150 μL of sodium phosphate buffer of pH 8.0 for 15 minutes at 25° C. After that 10 μL of pre-prepared butyrylthiocholine chloride (0.5 mM) substrate was added in the dark for 15 minutes, followed by the addition DTNB (0.5 mM), to produce thionitrobenzoate (TNB), whose absorbance range in 412 nm. 5-Thio-2 nitrobenzoate (TNB) (yellow color) anion was produced when thiocholine binds with DTNB which was measured in the form of absorbance in each well. Each compound was evaluated in triplicate at 0.5 mM.

Calculations of Inhibitory Activity

The enzyme inhibitory activity was calculated using the following formula:

Percent Inhibition=100−(O. D. of test/O. D. of control)×100

Where test is the enzyme activity with sample, and control is the enzyme activity without sample, and O.D. is optical density.

IC₅₀ Value Determination

The IC₅₀ values of the compounds were measured by monitoring the inhibitory effect of different concentrations ranging from 0.5-0.0125 μM for in-vitro butyryl cholinesterase activity. The IC₅₀ of the compounds was calculated using EZ-Fit Enzyme Kinetic Program (Perrella Scientific Inc., Amhrest, U. S.A.).

Kinetic Studies

Kinetics of two potent compounds 5 and 6 was done by using L-B reciprocal plots, designed by using GraFit software. 0.5 mM concentrations of each inhibitor, as well as control, were examined for their butyrylcholinesterase inhibitory activity using four different substrate concentrations (0.05, 0.1, 0.2, and 0.4 mM). Compound 5 show competitive inhibition, which indicates it binds with the active site of the enzyme. However, compound 6 shows non-competitive type of inhibition, which indicates it binds with the allosteric site of the enzyme.

Result and Discussion

4-Aminoantipyrine (A) and compounds 1-8 were evaluated for their in vitro enzyme inhibition activity against butyrylcholinesterase (BuChE) enzyme, results shown in table 1. Compounds 1, 2, 3, 5, 6, and 8 showed potent activities in the range of IC₅₀=0.0262±0.4 to 2.43±0.4 μM. In comparison to the standard drug, galantamine hydrobromide (IC₅₀=40.83±0.4 μM). However, compound 7, and 4-aminoantipyrine displayed lesser activity than the standard drug with IC₅₀=58.7±0.4 and 69.7±0.4 μM, respectively. Compound 4 was found to be completely inactive.

The limited SAR study reveals that position and nature of the halogen substituted on the phenyl ring plays a vital role in exhibiting the biological activity of the synthesized derivatives. Irrespective of the nature of halogens position 3 is found to be the most suitable in exhibiting the BuChE inhibition activity. On comparing the nature of the halogens present on the synthesized analogues 1-8, bromo is responsible for the higher activity as compared to chloro and iodo group.

In conclusion we identified 4-aminoantipyrine (A) and compound 7 as the moderate inhibitor of butyrylcholinesterase enzyme, while other derivatives 1, 2, 3, 5, 6, and 8 as potent inhibitors of butyrylcholinesterase enzyme.

TABLE 1 Structures of synthesized N,N′-disubstituted benzylamine derivatives of 4-aminoantipyrine, and their in-vitro butyrylcholinesterase (BuChE) inhibitory activity Butyrylcholinesterase Inhibition Activity IC₅₀ ± SEM μM Structures Ki ± SEM μM

IC₅₀ = 0.1 ± 0.2 μM

IC₅₀ = 0.5 ± 0.1 μM

IC₅₀ = 0.4 ± 0.3 μM

Not Active

IC₅₀ = 2.43 ± 0.4 μM Ki = 5.67 ± 0.5 μM Competitive Inhibitor

IC₅₀ = 0.7 ± 0.2 μM Ki = 2.4 ± 0.4 μM Non-competitive Inhibitor

IC₅₀ = 58.7 ± 0.4 μM

IC₅₀ = 0.0262 ± 0.4 μM

IC₅₀ = 69.7 ± 0.4 μM

IC₅₀ = 40.83 ± 0.4 μM Ki = 21.5 ± 0.7 μM Mixed type Inhibitor 

1. Eight new N, N′-disubstituted benzyl amine derivatives of 4-aminoantipyrine were synthesized, which posses butyrylcholinesterase inhibitory activity.
 2. Administration of a suitable dose of an inhibitor of butyrylcholinesterase enzyme selected from a group of 4-aminoantipyrine derivatives consisting of 4-(bis(3-chlorobenzyl) amino)-1,5-dimethyl-2-phenyl-1,2-dihydro-3H-pyrazol-3-one (1), 4-(bis(2-chlorobenzyl) amino)-1,5 -dimethyl-2-phenyl-1,2-dihydro-3H-pyrazol-3-one (2), 4-(bis(3-iodobenzyl) amino)-1,5-dimethyl-2-phenyl-1,2-dihydro-3H-pyrazol-3-one (3), 4-(bis(4-iodobenzyl) amino)-1,5-dimethyl-2-phenyl-1,2-dihydro-3H-pyrazol-3-one (5), 4-(bis(2-bromobenzyl) amino)-1,5-dimethyl-2-phenyl-1,2-dihydro-3H-pyrazol-3 -one (6), 4-(bis(4-bromobenzyl) amino)-1,5-dimethyl-2-phenyl-1,2-dihydro-3H-pyrazol-3 -one (7), and 4-(bis(3-bromobenzyl) amino)-1,5-dimethyl-2-phenyl-1,2-dihydro-3H-pyrazol-3-one (8) combined with suitable inert pharmaceutical ingredients, can be used for the treatment of Alzheimer's disease in humans. 